Clinical Research
Antiplatelet Therapy
Role of Reticulated Platelets and Platelet Size Heterogeneity on Platelet Activity After Dual Antiplatelet Therapy With Aspirin and Clopidogrel in Patients With Stable Coronary Artery Disease

https://doi.org/10.1016/j.jacc.2008.05.031Get rights and content
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Objectives

The aim of this study was to evaluate the relationship between reticulated platelets (RPs), platelet size, and platelet function in patients with stable coronary artery disease (CAD) taking aspirin and clopidogrel.

Background

Reticulated platelets are young platelets that are larger and possibly more active than non-RPs.

Methods

Flow cytometry was used to measure RPs after staining with thiazole orange and to define the upper 20% and lower 20% of platelets by size. Platelet aggregation was measured with light transmission aggregometry (LTA); platelet activation was assessed by measuring activated platelet surface expression of P-selectin and glycoprotein (GP) IIb/IIIa.

Results

Ninety patients were recruited and stratified into tertiles of %RPs. Patients in the upper tertile displayed greater platelet aggregation to 5-μmol/l adenosine diphosphate (ADP) (50.7 ± 16.4% vs. 34.2 ± 17.3%, p < 0.001), 1.5-mmol/l arachidonic acid (AA) (27.3 ± 16.9% vs. 11.7 ± 9.3%, p < 0.001), and 1-μg/ml collagen (18 ± 11.6% vs. 12.1 ± 8.7%, p < 0.05) and greater expression of GP IIb/IIIa (4.7 ± 1.8% vs. 3.1 ± 2.2%, p < 0.001). Frequency of low response to aspirin (AA LTA >20%) was higher in the upper tertile (53% vs. 17%, p < 0.001) compared with the lower tertile; low response to clopidogrel (ADP LTA >50%) was also elevated in the upper tertile (50% vs. 13%, p = 0.003). The larger platelet gate had a higher % of RPs compared with the smaller gate (15.4 ± 16.7% vs. 1.7 ± 2.3%, p < 0.001) and greater GP IIb/IIIa (5.7 ± 3.1 vs. 2.1 ± 1.2, p < 0.001) and P-selectin expression (7.8 ± 4.9 vs. 4.6 ± 2.7, p < 0.001).

Conclusions

The proportion of circulating RPs strongly correlates with response to antiplatelet therapy in patients with stable CAD. Large platelets exhibit increased reactivity despite dual antiplatelet therapy, compared with smaller platelets.

Key Words

aspirin
platelets
coronary artery disease

Abbreviations and Acronyms

AA
arachidonic acid
ADP
adenosine diphosphate
CAD
coronary artery disease
CHF
congestive heart failure
COX
cyclooxygenase
GP
glycoprotein
LTA
light transmission aggregometry
MPV
mean platelet volume
RP
reticulated platelet

Cited by (0)

Drs. Guthikonda and Alviar contributed equally to this work.